The fire safety industry is continuing to change rapidly and meeting the industry requirements for a smoke control system has become an ever-changing challenge. Research and development and design are essential elements for ensuring that required standards for new products as well as upgrades to existing ones meet the most up-to-date British Standards.
Smoke control systems are deemed an important part of the building’s safety equipment. This includes fire detection and fire alarm systems, automatic fire suppression systems, firefighting equipment including fire mains and firefighting lifts. They are classed as ‘Category 1’, which requires that all equipment manufactured for this purpose must be certified and tested to required standards.
The primary role of all smoke extraction and ventilation systems is to maintain a safe means of escape through all common areas of the building in a fire. This includes corridors and staircases which lead to a final place of exit for any occupants. Equally important is for those systems to assist the fire and rescue service to access and enter a fire zone and work safely.
Using the standards to manage smoke ventilation
To manage smoke ventilation effectively it is essential to determine the fire safety routes throughout the building. This should be done as early as possible following Document B Fire Safety guidance. However, the guidance may not be applicable in all circumstances and that’s where the use of Codes of Practice such as BS 9991, or taking a fire engineering approach can cover all scenarios. Early planning avoids later delays due to redesign and approval of the final building.
Also vital at an early stage is to decide what methods for smoke control are needed in the common areas of a building. Natural ventilation systems using façade vents and/or smoke shafts within the core of the building can be used in many cases. As can mechanical pressure differential systems requiring pressurisation or depressurisation of the escape routes and staircases.
Both depend on the budget and the space the building has to accommodate them. A natural smoke shaft requires a floor area of 1.5m² with no dimension less than 850mm. Mechanical ventilation requires a much smaller area of around 0.8m² as the air is forced through, but the extract system requires a primary and secondary three-phase power supply from two separate substations, which can be a challenge if space is an issue.
Meeting the design challenges
One of the most common challenges in designing smoke ventilation and control is correctly factoring in the distances people travel to escape. They are often exceeded at design stage, which leads to a fire engineered solution, adding a layer of cost and complexity to the project.
Another design consideration that can present design challenges is façade ventilation in corridors. This requires 1.5m² of free ventilation (usually in the form of a window), which is a large area of glazing to open and close especially in areas of high wind loads. In addition, an open vent creates a risk of fall and entrapment on closing.
Siting mechanical shafts can also be a challenge. Placement is often decided by the structural element of the build and may not be the best location for drawing smoke away from the stair core. If the shaft is located near the stair core in the event of a fire, it will be drawing air toward the stair rather than away and in doing so creates hazardous conditions for the fire and rescue service.
“Early planning avoids later delays due to redesign and approval of the final building.”
Issues can occur in a mechanical smoke extract ventilation system in the form of depressurisation. The air extraction needs to run at around 5–8m³/sec to ensure smoke is not being drawn into the stair. Failure to extract at this rate leads to excessive door pressures on apartment doors, preventing the occupants from opening them to escape. Air inlet should be considered carefully to prevent this and sensors that detect an increase in the pressure differential may be needed to reduce the fan speed. In some large corridors a secondary air inlet fan or shaft may be required.
Smoke control is at the heart of fire safety
It is important to not underestimate the structural and locational requirements of an effective smoke control system and building them into a design. Smoke control is as important as any fire safety equipment in the building and the most difficult to add in if left to a late stage in the design.
Appointing a specialist smoke control contractor as early as you can in the build programme and partnering with them ensures that a solution will be commissioned and accepted by LABC and FRS. Just as important is that at the handover stage, property managers ensure that the smoke control operation systems are clearly demonstrated and all operation and maintenance documents are provided.
“It is important to not underestimate the structural and locational requirements of an effective smoke control system.”